1. Field of the Invention
The present invention relates to a mounting apparatus and mounting method of mounting a flexible board onto a display board. Specifically, the mounting refers to electrically connecting terminal electrode rows. For example, the present invention relates to a mounting apparatus and mounting method of connecting a terminal electrode of a TFT (Thin Film Transistor) liquid crystal display and a terminal electrode of a TCP (Tape Carrier Package) of a flexible printed circuit board mounted with an LSI (Large Scale Integrated circuit) for driving.
2. Description of the Background Art
Referring to FIGS. 10 and 11, a conventional method of connecting a liquid crystal display 2 containing a liquid crystal layer 1 and a flexible printed circuit board 4 mounted with an LSI for driving will be described. In connecting, as shown in FIG. 10, a terminal electrode 3 of liquid crystal display 2 and a terminal electrode 5 of flexible printed circuit board 4 are bonded together, for example by thermocompression through an adhesive agent 6. For thermocompression, a cylinder-driven heater tool 8 is lowered and pressed.
FIG. 11 shows the structure of FIG. 10 viewed from above, where the terminal electrodes are bonded by thermocompression. It is generally known that flexible printed circuit board 4 stretches during thermocompression. It appears in FIG. 11 that terminal electrodes 3 and 5 are perfectly in alignment. However, it can be seen in FIG. 12, showing in enlargement outermost terminal electrodes 3 and 5, that terminal electrode 5 is displaced by a displacement amount 7 in the electrode width direction according to a stretch amount of flexible printed circuit board 4.
A common practice to adjust the stretch amount of flexible printed circuit board 4 is that an operator measures displacement amount 7 with use of a microscope or the like, and repeats thermocompression with different parameters of compressing temperature, pressure, time and so on to determine displacement amount 7. Thus, the operator must go through a continuing process of trial and error to find appropriate conditions for thermocompression.
Particularly, conventional terminal electrodes have a large pitch to allow for stretching of the flexible printed circuit board. In addition, a specific method of controlling the stretch amount of flexible printed circuit board has been unknown. For these reasons, in the conventional apparatuses, variation in stretch amount according to a material or size is restrained based on personal judgement and experience of an operator, for example, by varying an air flow as a variable parameter to adjust the lowering speed of a heater tool.
In recent years, flexible printed circuit boards are becoming more sophisticated and the pitch of terminal electrodes is reduced accordingly. This leads to the need for properly estimating the stretch amount of flexible printed circuit boards. Thus, the conventional mounting method is no longer satisfactory.
The above described conventional mounting technique suffers from three major problems.
First, the adjustment of the compressing temperature, pressure and time by cylinder-driven heater tool 8 is based on personal judgement and experience of the operator, whereby the stretch amount of flexible printed circuit board 4 is not quantitatively adjusted in the optimum manner with respect to the required adjustment amount. Depending on the skill level of the operator, such adjustment usually involves a considerable amount of time. Thus, the method is not satisfactory if the adjustment must be made in a short period of time.
Secondly, cylinder-driven heater tool 8 involves a long stroke. Thus, pressure variation in the cylinder is large and a load applied to an object fluctuates. Note that the compression pressure is obtained by dividing the load by an area subjected to compression. This causes variation is stretch amount and displacement inconsistency of terminal electrodes 3 and 5. As such, the conventional technique cannot fully cope with reduced pitches of terminal electrode rows to be connected.
Thirdly, the measurement of displacement amount 7 must be made by the operator with use of a microscope since an image processing apparatuses is unable to detect displacement amount 7 between terminal electrodes 3 and 5. The measurement involves a considerable amount of time. In addition, terminal electrode 5 of the flexible printed circuit board is usually formed by etching with a liquid agent and hence formed to have a section in a trapezoid shape as shown in FIG. 13. As a result, a measurement error of several μm is caused, for example depending on which of positions A, B and C the operator regards as the end of terminal electrode 5. Further, there is a variation in measurement result of displacement amount 7 due to a difference in stretch amount of terminal electrode 5 between compressed and non-compressed portions. Moreover, such manual measurement by the microscope does not immediately provide a distance between central lines of terminal electrodes 5 at both ends of the terminal electrode rows of flexible printed circuit board 4, i.e., a total pitch. Thus, feedback as well as real time elimination of variation in stretch amount are impossible.
In view of the above, the present invention aims at providing a mounting apparatus and mounting method which enables detection and adjustment of a stretch amount of a flexible printed circuit board in a short period of time, and which is capable of avoiding displacement inconsistency.